The instant invention relates to the transfer of images into plastic and more particularly to a method of applying a desired image of disperse dye to a plastic member.
While the technology relating to various types of plastic materials has developed greatly in recent years, the art relating to the application of colored images to plastic materials has remained somewhat undeveloped. In particular, the heretofore known art has failed to provide an economical method of applying images of high durability and resolution to plastic members. Methods wherein images are printed utilizing various techniques including screen printing have proven to be effective in many applications where image durability is not a primary concern. However, when conventional printed images are exposed to solvents or other corrosive environments, or when they are subjected to substantial frictional wear, they are unsatisfactory.
Sublimation printing wherein dyes are heated to their sublimation points to effect the transfer thereof to plastic members is also a widely known method of applying images to plastic members, although images produced by this method generally have poor resolution qualities. Such images also have poor thermal stability and poor resistance to solvents and other corrosive agents.
For applications where thermal stability, resistance to corrosion and wear, and high resolution are critical, it has heretofore been necessary to form images in two step molding processes. In a first step, a character image is separately molded in a desired configuration. Thereafter, the character is positioned in desired orientation in a second mold and the remainder of the member is molded around the character. Unfortunately, this method is extremely expensive and therefore has been used only where high resolution and durability are essential.
The instant invention relates to a novel and economical method of applying images of high resolution and durability to plastic members. Images formed by the method of the instant invention are not merely surface images but are actually diffused into the plastic of a member. This makes them durable and resistant to both wear and corrosion. In addition images formed by the method of the subject invention possess high qualities of resolution, light fastness and thermal stability. The method of the instant invention is also effective for forming high quality images having multiple colors in a single step. The method is comparatively simple and economical and hence has substantial advantages over the prior art methods.
In the first step of the method of the instant invention, an image of disperse dye is applied to the surface of a plastic member in a desired configuration. In the preferred method, this is effected by applying the dye to a paper sheet in the desired image, or more accurately, the mirror image thereof and then overlaying the paper sheet on the plastic member so that the dye image is in the desired orientation thereon and in intimate contact with a surface thereof. The dye is then diffused into the plastic of the member in accordance with the hereinafter described steps. It should be brought out, however, that only certain dyes can be effectively diffused into plastic in accordance herewith. Dyes which are suitable for the method of the subject invention generally comprise disperse dyes having melting temperatures which are below the respective thermal deflection temperatures of the plastic of the members to which they are to be applied and vaporization temperatures which are above said thermal deflection temperatures.
In the second step of the method, the dye and at least the portion of the plastic member which is adjacent thereto are heated to a temperature which is above the melting point of the dye but below the thermal deflection temperature of the plastic although high enough to cause at least some surface softening of said plastic. Thereafter, the dye is allowed to diffuse into the plastic to impart the desired dye image thereto. This provides a sharp, clear image which is resistant to solvents and the like, possesses high wear resistance qualities and possesses high qualities of thermal fixation and light fastness. Hence, the method of the instant invention is effective for making image bearing plastic members of very high quality. The method is also simple and economical and therefore has substantial advantages over the methods of the prior art.
For these reasons, it is a primary object of the instant invention to provide an economical method of applying high quality images to plastic members and the like.
Another object of the instant invention is to provide a method of applying high quality dye images to plastic members.
A still further object of the instant invention is to provide a method of applying dye images to plastic members and the like so that the images thereby formed exhibit qualities of high resolution, high resistance to wear and solvents, high light fastness, and high thermal fixation.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawing.